- Air Lock
Air trapped in between liquid columns.
- Air supply
Control final elements (control valves, actuators etc.) are powered pneumatically and usually requires 6-8 bar clean dry air for functioning. A separate air header (pipe) is maintained to provide this to control components in the field.
Denotes vibration / movement horizontal to axis or shaft
No proper passage. Obstruction by a foreign material.
- Cable tray
Safer and neat routing of cable in the field is done through metal trays called cable tray.
Compressor Discharge Pressure. Denotes the pressure to which inlet air is compressed by a gas turbine. Sometimes called PCD by different manufacturer of gas turbines.
Accumulation of sediments or formation of hard particles preventing passage of process fluid.
- Control Valve
Device to enable change in process flow of liquid or gas.
Device, that can compare a set point and a measured variable to give a corrective output.
Denotes differential pressure. Flow measuring by orifice plate uses pressure difference sensing unit called D/P cell.
Elastic partition in actuator to allow pressures sensing and corresponding movement of a plate or disc supporting the diaphragm.
Gas producer. Referring to the inlet air compression stage in a gas turbine. Sometimes called as gas generator or ‘GG’.
Electric power being connected unintentionally to earth or zero potential.
A display or alarm indication occurring when the actual ‘PV’ values is not increasing or decreasing. Means the display is not following the actual value of PV.
Denote the display stays either at maximum or minimum of scale when PV is actually within the range. Failed to respond to process.
- Failure: Complete absence of display or a system.
- Heat Switch
Device that gives an open or close contact when exposed to heat above a pre set value.
The display of ‘PV’ is oscillating in regular interval across set point.
- Hydraulic head (static)
Pressure exerted by a liquid column at its base is called static head.
A display on panel or screen giving the engineering unit of the process variable corresponding to physical value of variable.
- Impulse lines
Process variables are connected from process tapping to the measuring instrument with tubes called impulse lines for measuring pressure, flow etc.
Fluctuating. Not corresponding to actual value.
- I to P converter
Device to convert electrical signal to a proportional pneumatic (air) signal.
Junction box encloses the terminals connecting cables from individual instruments in the field to a multicore cable routed to control room.
Succession of any set of events after process satisfies a predetermined set of conditions.
- Lost Control:
The actual value of ‘PV’ is increasing or decreasing away uncontrollably from set point (desired variable) without responding to controller out put.
Motor operated valve (Generally electrical)
- OK lamp
Usually a green lamp on the face of an instrument to indicate the circuit is healthy.
- On-line /Live
Any instrument which is powered and is physically connected to process.
- Over ride
Part of protection logic of process being allowed to skip (bypass/defeating its function) with permission of operation people.
Device that generates signals when in contact with variables like speed, vibration.
A position balance device to maintain the stem movement of a control valve to a corresponding controller output signal.
- Power Supply
Instrument component make use of 24VDC for operation. A rectifier and a battery back up are maintained to give instruments the required electrical power.
- Process Variable
Active component of physical or chemical status of process variables usually, levels, pressure, flow, temperature, pH etc.
Power Turbine. Referring to the out put shaft drive of a gas turbine.
- Quick Bleed (Quick went)
Device which bleed off in large volumes the pressure in an actuator to make faster operation depending on its signal.
Denotes vibration / movement vertical to axis or shaft.
The limits (zero to maximum) of variable with in which the instrument works.
Device, which continuously registers the variable value on a scaled chart.
- Relay (Electrical)
Electromagnetic device that makes or breaks a set of contacts when operated electrically.
- Relay (Pneumatic)
A pneumatic device that amplifies the volume of air output according to input signal it receives.
Resistance Temperature Detector. Device that changes its resistance proportional to the temperature it is exposed.
- Safety Barrier
Inter-face device between field and control room limiting energy going to field to prevent spark in hazardous area.
SUPERVISORY CONTROL AND DATA ACQUISITION.
- Electronic remote monitoring and transmission of parameter values and status of equipment.
- Set point
The desired value of the process parameter decided for normal operation.
- Solenoid Valve
Electro-magnet assembly electrically operated to actuate valve plug or similar end elements.
Thermostat or temperature switch. A device with a contact that close or open at a pre set value.
Thermocouple. Device that generates Electro motive force in the rage of millivolts, when installed in temperature different than ambient temperature.
Limiting the fuel flow to gas turbines when speed or temperature of engine exceeds a pre set value.
An electronic device that will allow delayed logic functions.
The process variables are obtained from process through small connections or tapping on the process piping.
Primary sensing device that can convert one form of energy to another form or measure.
Device sensing the process variable and sending proportional signal to control room.
Ultraviolet radiation. Used to detect fire.
- Valve gland
Area of a control valve where the process fluid is prevented from leaking to the atmosphere though there is physical (stem) movement required at the place of interface between process and atmosphere.